Flying spot camera tube



.1. A. RADo Nov. 28, 1961 INVENTOR.

3,011,019 FLYDIG SPOT CAMERA TUBE .lohn A. Rade, Lancaster, hio, assigner to Diamond Power Specialty Corporation, Lancaster, Ohio, a corporation of h10 Filed Oct. 20, 1958, Ser. No. 768,276 6 Claims. (Cl. 178-7.1)

This invention pertains to an improved translating device for developing an electrical signal corresponding to a light image without the use of an electron beam.

One important object of the present invention is to provide an improved electronic camera device.

Another object is to provide an improved device for deriving an electrical signal from a light image, the device being of improved simplicity and ruggedness of construction.

Another object is to provide an improved device of the above-described character in which an electrical signal is developed by means of a flying spot of light.

Another object is to provide an improved device of this character including a screen for receiving alight image upon one face and means for developing a video signal representing the light image by scanning the reverse face of the screen with a light spot.

Another object is to provide an improved electrical camera device which does not require an evacuated envelope.

Another object is to provide an improved device of this character having a screen including two photoconductive films separated by a conductive mosaic, whereby electrical charges on the individual elements on the mosaic may be controlled by a light image projected upon one of the photoconductive films and also by a ying spot of light projected upon the other one of the photoconductive lms in such a way as to generate a video signal.

Still another object is to provide an improved device of this character including a photoemissive film superimposed upon a photoconductive film whereby a video signal can be generated by projecting a light image upon the photoconductive lm and by scanning the photoemissive iilm with a iiying spot of light.

These and other objects and advantages of the present invention will become apparent in the following description of representative embodiments thereof taken in conjunction with the drawing wherein:

FIGURE l is a schematic cross-sectional view of a ying spot camera device according to a first embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a flying spot camera dev-ice generally similar to the device shown in FIG. l but including insulating material interposed between the conductive elements of the charge bearing mosaic; and

FIG. 3 is a schematic cross-sectional view of another embodiment of the invention incorporating a photoemissive film in place of the second photoconduotive film shown in FIGS. l and 2.

A video camera device according to the present invention includes a screen having front and back light responsive surfaces, electrode means for making electrical contact to both of the surfaces, and electrical charge storage means disposed between the front and bac-k surfaces for storing electrical charges in a mosaiclike pattern. A light image is projected upon the front surface of the screen, and the back surface yis scanned by a flying spot of light. The front and back surfaces are maintained at different electrical potentials, so that current flows into and out of the storage means responsively to the light image and -to the iiying spot. The

nited States Patent 3,011,019 Patented Nov. 28, 1961 icc flying spot causes the storage means to become charged to a predetermined potential, and the charge leaks out of the storage means at a rate determined by the local area illumination provided by the light image. The amount of charging current is proportioned to the light image, and represents a video signal.

In the preferred embodiment, both the front and the lback surfaces of the screen are constituted of photoconductive material, while in the alternative embodiment described herein, one of the surfaces is photoemissive and the other is photoconductive.

It will be appreciated that the drawing is not to scale and that certain portions thereof are greatly enlarged beyond their normal scale proportions in order to show clearly the various elements of the devices, which if they were shown according to scale would be diliicult to dis- Referring now to FIG. 1, a flying spot camera device is shown therein, and includes front and back face plates 10 and 12, respectively, which are transparent and may ybe made of glass. The face plates 10- and -12 are preferably of optical quality and are smoothly finished in order lto minimize distortion. Bus bars 14 and 16, which may be of any desired highly conductive material, such as gold, silver or copper, for example, extend peripherally around the face plates 10 and 12, respectively, preferably on the inner surfaces IIS and 20 thereof. The bus bars contact transparent electrode films 22 and 24, respectively, which extend over the inner faces 18 and 2li of the two face plates. The electrode films 22 and 24 may be of any desired electrically conductive transparent material, and are preferably of the tin oxide type of the kind commercially designated by the trade name Nesa having a surface resistivity of less than ohms per unit square.

vPhotoconductive films 25 and 26 are disposed upon the electrode iilms 22 and 24, respectively, and are spaced apart by a mosaic 3d composed of relatively small elements 32 of a metal such as silver. The photoconductive films 25 and 26 may be made of any desired photoconductive material, preferably one having a relatively high dark-to-light conductivity ratio such as, for example, arsenic selenide, antimony trisultide, or semiconductive germanium or silicon. They are preferably relatively thick and may be, for example, one micron or greater in thickness in order to minimize the transmission of light thro-ugh them, so that, yfor example, the light image projected upon the front photoconductive -ilm 25 will not be transmitted to any large degree to the reverse photoconductive iilm 26. The actual thickness of the photoconductive films 25 and 26 will of course depend upon such factors as the intensity of illumination to be used, and the light transmission characteristics of the material of which they are made.

All of the films, including the mosaic iilm- 30, may 'be succesively applied upon either one of the two face plates 10 and 12, respectively, and the sandwich then completed by the application of the second face plate. Electrical leads 34 and 36 are connected to the bus bars 1'4 and 16,.-respectively, -for connecting the device in an eX- ternal circuit, and the device is sealed by the application of an insulating sealing material 40 around the edges:

conductive, and thereby causes the mosaic elements 32 toV `become charged tothe potential of the back electrode film 24.

i Considering any one of the mosaic elements 32, after lit has been charged and the scanning light beam has moved away from it, it discharges through the front photoconductive yfilm a-t a rate determined by the conductivity of the film 25 in the area immediately adjacent to mosaic element 32. The conductivity of each small area portion of the front photoconductive film 25 is determined by the amount of light falling upon it. During the interval, therefore, that the light beam 44 is absent from the vicinity of a particular element '32, theelement discharges exponentially toward the potential of the front electrode film 22 at a rate dependent upon the illumination of the front photoconductive film 25 in the region thereof immediately adjacent to the mosaic element 32. The value of the chargeY remaining upon theielement 32 at the time the light beam `44 next approaches it is therefore determined by the local illumination of the front photoconductive fil-m 25, and the remaining charge determines the amount of current required to recharge the element 32 to the potential of the back electrode film 26 upon the succeeding scan of the light beam 44. The recharging current iiows through the output resistor 42 and produces a' video voltage pulsev of a magnitude proportional tothe illumination. The total video signal is made up of a succession of such pulses. An appropriate time constant is incorporated in the circuit to which the device is connected so that the video signalV is not masked by the discharge current of the individual mosaic elements 32. Y

A modified form of the preferred embodiment of the invention is illustrated in FIG. 2, and is exactly similar to the form hereinabove described in connection with FIG. 1 except that the individual mosaic elements 32 are separated by an insulating network 50 instead of being air-spaced. The camera device shown in FIG. 2 may be made by first depositing the front transparent electrode film 22'and the front photoconductive llm 25 Aupon the lfront face plate 10, and then placing a fine mesh glass screen upon or immediately adjacent to the Vfront photoconductive film 25 and evapora-ting a conductive material such as silver through the screen and upon the photoconductive lm 25 in sufficient quantity to llu'p the interstices of the screen. After this is done,

' the conductive material that has beend'eposited upon the screen itself may be groundy off, thereby isolating 'each little one of the mosaic elements 32 in a separate interstice in the screen. The back photoconductive film 26 and the' back electrode lmV 24 are preferably deposited upon the mosaic 30, but alternatively they may be deposited on the back face plate 12, which is then pressed upon the mosaic, so thatthe back photoconductive film 26 makes contact with the individual elements '32 of the mosaic.

Alternatively, the mosaic 30 may-be evaporated through' a reticule (not shownl'which'is supported closely adjacent to the front photoconductive film 25, and then after the evaporation is completed and the individual mosaic has been deposited upon, the reticule itself lmay Vbe lremoved -by etching'or the like and the reticule maythen 4 be applied to the photoconductive layer, fitting itself over the individual, previously evaporated conductive elements 32.

The theory of operation of the device illustrated ini FIG. 2 is exactly similar to the operation of the devicel shown in FIG. l. Neither one of these devices requires an evacuated envelope or electron gun. lThey are ex tremely simple to manufacture, of rugged constructiom. and dependable in operation. A camera device accord-- ing to another embodiment of the invention is shown in BIG. 3, and includes a front face plate 6, the inner sur-V face of which is coated with a transparent electrode film 62. Contact with the electrode film 62 is made by a. peripheral bus bar 64. A photoconductive film 66 is disposed upon the electrode film 62', and a photoemissive film 68 is disposed on top of the photoconductive hlm 66. The electrode film 62 may be of metal, or, preferably, of Nesa. The photoconductive film 62 may be of arsenic selenide', antimony trisulfide, or semiconductive germanium, or silicon as desired. The photoemissive film 68 may be o-f any desired photoemissive `material and if its volume resistivity is relatively low, the film 68 is preferably made in mosaic form as shown. It, for example, the photoemissive film 68 is made of cesium-oxide-silver, it is madein a mosaic having relatively small elements 7 t) which are spaced apart slightly from each other, thereby providing the desired degree of volume resistivity and effectively insulating the separate elements from each other. If the resistivity of the photoemissive material is suiiiciently high, the filmv 68 may be made continuous. The back face plate 72 of the device is coated on its inner surface with a'transparent, conductive electrode. film 74, preferably of Nesa, and electrical contact is: established ywith the vfilm 74 by means of a bus bar 76 which extends peripherally around the back yface plate 72. The front and back face plates and 72 are sealed to opposite ends, respectively, of a cylindrical enclosuremember 78, which is of an insulating material such as glass, and the interior of the chamber so formed is evacuated. Y r

For oper-ation, the device is connected in a circuit as. shown including a direct current voltage source 41 and an output resistor 42 connected in series between the front and back bus bars 64 and 76, respectively. The voltage source 41 is connected in a direction to malte the 'back electrode film 74 positive with respect to the front electrode film 62 so that photoelectrons emitted by the photoemissive film 68 are attracted toward and drift to the back electrode film 74 where they are collected. A light image is projected upon the photoconductive film 616,'and a scanning light beam 44 is projected through the back face plate 72 upon the photoemissive film 68. When the light beam 44 strikes a given elemental area portion of the photoemissive film 68, that portion acquires a positive charge due to the photoemission of electrons therefrom. After the light beam departs, the charge decays lby conduction through the photoconductive film 66 ata rate determined by the illumination falling upon the corresponding area portion of the photoconductive film 66. The current required to recharge the particular area portion of the -photoemissive film 68 upon the next pass of the scanning light beam 44 produces a video voltage signal across the 1output resistor 42. v

What isA claimed is: Y 1). A Aphotoelectric device for :generating a video signal comprising a photoconductive lm, means for projecting a light image uponsaid Vphotoconductive film, a photoemissive film disposed upon and electrically in contact with one face of said photoconductive film, means for scanning said photoemissive film and for causing an emission of 4electrons therefrom, means for collecting photoemitted electrons from said'photoemissive film,

I Vand a transparent electrode extending over the face of said photoconductive film opposite'vfrom said photoemissive film.

2. An electrical camera device for generating a video signal comprising a photoconductive film, means for projecting `a light image upon said photoconductive film, a photoemissive film disposed on said photoconductive film, means for scanning said photoemissive film and for causing an emission of electrons therefrom, means for collecting photoemitted electrons from said photoemissive film, and means for electrically contacting theI surface of said photoconductive film opposite from said photoemissive til-m.

3. An electrical camera device for generating a video signal comprising a photoconductive film, means for projecting a light image upon said photoconductive film, a photoemissive film superimposed `directly upon said photoconductive film and having `a relatively high lateral resistance and a relatively low thickness resistance, means for scanning said photoemissive iilm and for causing an emission of electrons therefrom, means for collecting photoelectrons emitted by said yphotoemissive film, and electrical contact means for making area contact With the surface of said photoconductive film opposite from said photoemissive ilm.

4. An electrical camera device for producing a video signal responsively to the concurrent application thereto from opposite directions of a light image and a moving spot of light comprising a laminar structure including a photoconductive film having front and back surfaces and arranged to receive the light image upon its front surface, a transparent electrode disposed on the front surface of said film for making electrical contact therewith, a photoemissive film having relatively high lateral resistance and relatively low thickness resistance disposed on the hack surface of said photoconductive iilm and arranged to he scanned by the moving spot of light, means for collecting photoelectrons emitted by said photoemissive film responsively to the moving light spot and thereby successively charging small area regions of said photoemissive film to a predetermined potential, and

means for individually discharging the small area regions of said photoemissive lm through said photoconductive iilm at a rate determined by the intensity of illumination of the light image projected upon said Photoconductive nlm in separate portions thereof immediately adjoining the small area regions of said photoemissive film.

5. An electrical camera device for producing a video signal responsively to the concurrent application thereto from opposite directions of a light image and a moving spot of light comprising a laminar structure including a photoconductive lm having front and back surfaces and arranged to receive the light image upon its front surface, a transparent electrode disposed on the front surface of said film for making electrical contact therewith, a photosensitive surface comprised of a mosaic of photoemissive elements disposed on the 'oack surface of said photoconductive film and arranged to be scanned by the moving spot of light, means for collecting photoelectrons emitted by said photoemissive mosaic responsiveiy to the moving light spot and thereby successively charging the areas by each of said photoemissive elements to a predetermined potential, and means for individually discharging said areas by each of said photoernissive elements at a rate determined by the intensity of illumination of the light image projected upon said photoconductive film in the area of each of said photoemissive elements.

6. The invention as claimed in claim 5 wherein said matrix of photoemissive elemental areas is a continuous photoemissive film.

References Cited in the file of this patent UNITED STATES PATENTS 2,732,469 Palmer Jan. 2,4, 1956 2,826,632 Weimer Mar. 1l, 1958 2,899,488 Kalfaian Aug. ,11, 1959 2,929,866 Melamed Mar. 22, 1960 

